This invention relates to noninvasive physiologic condition sensors, and more particularly, to noninvasive oximetry sensors.
Noninvasive oximetry commonly takes advantage of the difference in the light absorption coefficient of hemoglobin and oxygenated hemoglobin with respect to light in the red and infrared ranges. This type of oximeter normally includes sensors that are placed against patient tissue which is well profused and includes sources for emitting light at one or more wavelengths into the tissue and a light detector for detecting the amount of light which passes through the tissue. The amount of light absorbed at each wavelength is used to calculate oxygen saturation in the patient's blood in accordance with Lambert-Beer's law. Such sensors are normally placed on the fingertip, earlobe, nasal septum or forehead of the patient and preferably include means for retaining the sensor in position for the extended periods during which such measurements are made.
One type of prior art pulse oximetry sensor is disclosed in U.S. Pat. No. 4,830,014 and includes an emitter and detector mounted on an adhesive pad for being secured to the patient. Leads are connected to the emitter and detector for connection to a monitor. For sanitary reasons, such sensors are normally disposable.
A similar type of sensor is shown in U.S. Pat. No. 5,209,230 wherein the emitter is mounted on a disposable adhesive pad and the detector is mounted in a housing which is detachable from the pad to permit reuse. The per use expense of such prior art sensors is relatively high because either one more of the components, such as, the emitter, the detector, the connector, or the cable are commonly discarded after a single use.
To insure accurate results, it is desirable that the emitter and detector be positioned in an opposed relation on the opposite side of the patient's finger or earlobe. For this purpose, prior art oximetry sensors commonly include alignment markings printed on the outer surface of the adhesive pad. However, these alignment marks may not always be clearly visible on both sides of the finger or earlobe simultaneously and in more than one perspective which makes alignment more difficult.